Synthesis, Characterization, and Reaction Chemistry of tert-Butyl Hypofluorite

tert-Butyl hypofluorite ((CH₃)₃COF) can be synthesized by the low-temperature reaction of elemental fluorine with tert-butyl alcohol dissolved in propionitrile or acetonitrile. The isolated compound, which melts around –94 °C and has an extrapolated boiling point of about +40 °C, has been characterized by mass, NMR, and IR spectrometry. The ¹⁹F NMR shift of +67 ppm lies between the corresponding shifts of HOF and CH₃OF and implies a rather high O-F bond energy. Although sterically crowded, tert-butyl hypofluorite adds to olefins to form β-fluoro-tert-butoxy compounds. Addition is mainly in an anti mode, and the regioselectivity corresponds to the action of a hitherto unknown tert-butoxylium electrophile. Also formed are adducts containing F and CH₂CN, the latter deriving from the acetonitrile solvent.